This invention generally relates to liners for aircraft engines. More particularly, this invention relates to an acoustic liner including acoustically inactive areas for attenuating noise generated by an aircraft engine.
An aircraft engine typically includes a plurality of fan blades that rotate within an engine case. The engine case includes an acoustically active lining forward of the fan blades to reduce the level of noise emitted from the aircraft engine. Conventional acoustic linings include a face sheet covering a honeycomb structure. Acoustic energy generated by rotation of the fan blades is transmitted through a plurality of openings in the face sheet to the honeycomb structure where the acoustic energy dissipates to provide an overall noise reduction.
Openings in the face sheet provide for the transfer of acoustic energy into the honeycomb structure. Therefore conventional acoustic liners are arranged to minimize splices, seams and other disruptions that prevent transmission of acoustic energy through the face sheet and scatter the noise energy into lower order acoustic modes that are difficult to attenuate by the liner. However, a splice free face sheet or honeycomb structure is not practical and minimizing the area of a splice or acoustically dead area of an acoustic liner requires efforts that in many instances are disproportionate to any realized benefits.
Accordingly, it is desirable to develop and design an acoustic liner that provides improved sound attenuating characteristics without the need to minimize or eliminate acoustically inactive zones.